The present invention relates to an electrodeless microwave-generated radiation apparatus for exciting a lamp containing emission material such as mercury by the use of microwave energy to emit radiation in the ultraviolet portion of the spectrum.
In recent years, ultraviolet radiation has been widely used for carrying out painted surface processes such as curing of ultraviolet-cured-type adhesive or ink, or photochemical reaction of chemical materials, and the like. As an apparatus for emitting such ultraviolet radiation, there has been used an electrodeless microwave-generated radiation apparatus wherein a lamp containing emission material such as mercury is excited by the use of microwave energy to emit ultraviolet radiation. Improvement in the radiation apparatus has been made and disclosed in, for example, U.S. Pat. No. 3,872,349, U.S. Pat. No. 4,042,850, U.S. Pat. No. 4,359,668 and U.S. Pat. No. 4,504,768. This kind of electrodeless radiation apparatus is shown in FIGS. 8a and 8b, in which FIG. 8a is a longitudinal sectional view of the apparatus and FIG. 8b is a sectional view taken along the line B--B of FIG. 8a. As shown in FIGS. 8a and 8b, there are provided in the apparatus a lamp 1, a microwave cavity 2, a reflector 3 made of metal material to define the microwave cavity and having a concave or elliptical shape in cross section for converging emitted radiations in a radiating direction, and slots 4 as coupler means for supplying microwaves generated by magnetrons 5 (microwave generators) to the microwave cavity 2 via waveguides 6. Also, there is provided a mesh 7 defining a wall of the microwave cavity 2 for transmitting emitted ultraviolet radiation. The mesh 7 acts as a short-circuit plate for microwaves while it acts as a transmitting medium for light. Numeral 8 is a blower for controlling the heat generated by electrical discharge, and more particularly for cooling down both lamp 1 and reflector 3 with air flow through vent-holes 9 provided in the reflector 3. Numeral 10 is an ultraviolet radiation bulb which serves as a source of ultraviolet radiation for initial ionization in order to trigger the formation of plasma in the lamp 1 when microwaves are introduced into the microwave cavity 2.
In the above-mentioned apparatus, when the magnetrons 5 are operated and microwave energy generated thereby is coupled to the microwave cavity 2 through the slots 4, microwave energy excite emission material such as mercury vapor contained in the lamp 1. Ultraviolet radiation from the ultraviolet radiation bulb 10 triggers electrical discharge in the lamp 1 to emit ultraviolet radiation. The lamp 1 is located at a focal point of the elliptically surfaced reflector 3 and thus, while a portion of the radiations emitted in all directions is directly transmitted through the mesh 7, the remaining radiations emitted in the opposite direction (upward direction) and lateral direction are reflected on the reflector 3 and advance towards the mesh 7. Therefore, an object to be processed will instantly be processed (e.g. dried and cured) when disposed beneath the mesh 7. A large number of objects can be processed continuously if they are moved successively by a belt conveyor or the like.
In the electrodeless radiation apparatus, mercury which is likely to emit ultraviolet radiation is contained in the lamp 1 since the apparatus aims at processing objects by ultraviolet radiation. The generation of visible radiation and infrared radiation besides ultraviolet radiation is, however, inevitable so that the temperature of the lamp 1 under operation becomes considerably high. Thus, in order to protect the lamp 1 from being damaged at a high temperature and avoid overheat of the reflector 3 and objects to be processed, air is supplied inside the microwave cavity 2 by the blower 8 through the vent-holes 9 provided in the reflector 3 to cool the lamp 1.
In the conventional apparatus having the abovementioned structure, microwaves supplied into the microwave cavity 2 are repeatedly reflected in the microwave cavity 2 at random and not properly converged on the lamp 1, so that it takes more than several tens seconds till emission of ultraviolet radiation becomes stable. Thus, the conventional apparatus has a drawback that harmful ozone gas generates or reflected microwave damages the magnetron till emission of ultraviolet radiation becomes stable. In addition, objects to be processed are overheated due to infrared radiation or visible radiation.
The present invention was made to solve the above drawbacks, and it is an object of the present invention to provide an electrodeless radiation apparatus which can effectively couple microwave energy to a lamp so that the time required for stabilization of the emission of ultraviolet radiation is shortened, and which can reduce undesirable radiation such as infrared radiation.